GROUND ICE.
(Vol. v., p. 370.)
Your Querist J. C. E. is informed that the singular phenomenon of the formation of ice in the beds of running rivers has not escaped the notice of scientific observers. M. Arago has devoted a paper to its investigation in the Annuaire du Bureau des Longitudes for 1832 or 1833, in which he specifies the rivers in which it has been observed. Indeed, although from its nature it is likely to escape notice, it is probably of not infrequent occurrence. Ireland, in his Picturesque Views of the Thames, quoting Dr. Plot, speaks of the subaqueous ice of that river. Colonel Jackson, in the fifth volume of the Journal of the Royal Geographical Society, alludes to its formation in the Neva, in a paper on the congelation of that river; and in the following volume of the same Journal is an article by Mr. Weitz, especially devoted to the ground ice of the rivers of Siberia. More recently, Mr. Eisdale has contributed the result of his researches upon the same subject to the Edinburgh New Philosophical Journal, vol. xvii.; and, finally, Dr. Farquharson has made public his observations upon the ground-gru of the rivers Don and Leochal, in Lincolnshire, in the Philosophical Transactions for 1835. There is also an article on the subject in one of the later volumes of the Penny or Saturday Magazines.
That bodies of running, water, the surface of which solidifies when exposed to a diminished temperature, should have a tendency to congelate in their sheltered depths, seems an anomaly which demands inquiry and explanation; and accordingly each of the above-mentioned writers has raised an hypothesis more or less probable, to account for the phenomenon. Dr. Farquharson would attribute it to the radiation of heat from the bottom, as dew is formed by radiation from the surface of the earth; but a consideration of the supervening obstacles to radiation—a body of moving water thickly coated with ice and even snow—destroys the plausibility of his theory. That of Mr. Eisdale, that the frozen spiculæ of the atmosphere falling into the water become nuclei, around which the water at the bottom freezes, seems merely frivolous. The explanation of M. Arago is more satisfactory, viz. that the lower currents of water being less rapid in motion than those intermediate, or at the surface, congelation may be expected at a lower temperature (say 32° Fahr.), the process of crystallisation being favoured by the pebbles, fragments of wood, and the uneven surface of the river's bed. After all, however, the phenomenon has been but imperfectly investigated under its various manifestations, and its real cause probably remains yet to be discovered.
William Bates.
Birmingham.
For an explanation of this occurrence, I would refer J. C. E. to Whewell's Astronomy, Bridgewater Treatise.
Unicorn.